I'm currently designing a sub which rolls off 8db from 100Hz to 20Hz but I want to alter the design to account for room gain. I'd like to use a generic transfer function that I could use to at least guess-attempt a flat in-room response.

Eg. 6db/octave below 80Hz, for a room approx. 4m x 3m x 2.5m?
I think even a crude approximation would be helpful.

Or since the transfer function is a result of the room dimensions (and volume?), does someone have a fomula to calculate it?

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"The human mind is so constituted that it colours with its own previous conceptions any new notion that presents itself for acceptance." - J. Wilhelm. (But I still think mine sounds better than yours.)

One of our members, Serow, has made a file that can be added to Subwoofer Simulator, a loudspeaker modelling program written by our own F4ier, to display a louspeaker response with and without room gain. I'll dig up the post for Serow's file, if you like.

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"A friend will help you move. A really good friend will help you move a body."
-Anonymous

Just for the heck of it, here is a simulation of a Peerless XLS 12" , (3.5 ohm Re), in a 1 cu ft box tuned to 25 Hz. 28.3 volts driven, (app 200 watts for a 4 ohm speaker). This simulation program is Subwoofer Simulator with Serow's room gain file added.

Upper green line is response with room gain.
Lower green line is response without room gainl
Orange line is impedance.
Purple line is cone excursion.

According to that graph, a crude transfer function is 2db/octave, and my anaechonic design averages 3.3 db/octave below 100Hz which means that, although not perfect, it helps a bit in flattening out the overall FR.

KW, funnily enough, I'm designing for a 10" XLS and 1 passive.

Bill, I'm well aware, but better to have some approximation included in the design then none at all, as room gain will always be apparent.

I'd love a function on how to calcuate the gain based on dimensions...

__________________
"The human mind is so constituted that it colours with its own previous conceptions any new notion that presents itself for acceptance." - J. Wilhelm. (But I still think mine sounds better than yours.)